I put one on my 44mag that worked with the factory 3-48 screw, I used blue loctite under the shotgun shorty ramp cuz I had it, but Black Max 380 might be a better choice, it works by itself with no screws in the WGRS if the sight base is lapped to the barrel for a closer fit. Brownell's may have longer 3-48 screws. You may be able to get one from H&R if you don't have the original. The other option is to drill it out and tap it to 6-48, with a predrilled hole, it wouldn't be hard if you're careful, then all you would need is a 6-48 bottom tap, Brownell's does have them, I just ordered another one from them not too long ago.
Tim